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How do airliners cross the ocean without GPS?
How do airliners cross the ocean without GPS?
Do they use dead-reckoning or are there navigation aids floating out there?

It's worth noting that ICBMs cross the oceans on combination of INS (as mentioned in some answers) and automated star tracking devices data (as it will be unwise to rely on any sort of ground/satellite assisted navigation during the global nuclear meltdown). Same applies to many military planes, such as a venerable SR71 (which was equipped with a daylight capable star tracker).

@oakad The U-2 also used celestial navigation, especially when flying  close to the north pole, which they often did to see what the USSR was doing at it's far-northern nuclear test sites. During the early stages of the Cuban Missile Crisis, one of these flights accidentally crossed the Russian far-east after the pilot miscalculated his return to Alaska.

Well, most airlines do cross the ocean with GPS in today's world.
That being said, most (if not all) transcontinental airliners, and many flying domestic routes as well, have what's called an inertial navigation system (a form of dead-reckoning where gyros and accelerometers are used to compute changes in position and attitude). The INS feeds into the flight management computer which is used to cross-check the GPS position, and can be used as a primary navigation source should the GPS signal be lost or corrupted.
Prior to GPS, inertial navigation was the primary means of navigating across oceans. However, a great many airplanes did cross oceans before INS... with varying success. The general idea was to use a combination of dead-reckoning, radio beacons where you can find them (small islands and coastlines), the sun (with the help of a sextant) during the day, and the stars at night. Hopefully, this puts you in position after some period of time to pickup ground-based navigational aids, or to identify a coastline. This actually works pretty well if your wind estimates are good, and the margin for error is high enough. As DeltaLima points out, long-range radio navigation systems also started to emerge around World War II (LORAN and Decca) which had a much greater range than previous radio beacons, and therefore decreased the amount of time required to fly by dead-reckoning alone. By the time inertial navigation became prevalent in the 1970's, airlines were already providing reliable transcontinental passenger flights every day.
Another possible outcome is that your plane is lost in the ocean, never found, and the Discovery Channel funds an expedition to look for you 75 years later.

Many aircraft, the Vulcan included (first hand experience) have a sextant protruding from the fuselage.  The navigator would take star fixes - just as the Vikings did when they crossed the Atlantic.

Do i read correctly that planes don't have compasses?

@atk No, a compass is required equipment on all certified airplanes.

@atk Note that the usefulness of copmasses decreases as you get close to the poles, which some intercontinental flights do.

@Simon: The upper windows on earlier 737s and other airliners of that era served the same purpose.

@atk.  How would a compass help with an oceanic crossing since you want to fly a great circle route?

@Simon it would help you maintain a particular heading for a given amount of time.

An aeronautical engineer with Airbus once boasted to me that the IMU on new Airbuses would localize the aircraft to within 3 feet after a cross-country flight, without any GPS input other than the starting location.

@Chris "Cross country" and "airbus" might mean the width of France - about 1,000km and 3 hours, the width of the UK (smaller) or the width of the US or USSR.  Any would indicate good accuracy for an INS, but the statement is rather ambiguous.

@AdamDavis yeah, I wish I could have gotten more specific info from him. It was at a US facility so I'm going to guess he meant across the US, but I can't say for sure, sorry!

@atk: a compass is an inefficient guide to crossing an ocean. If you take off from the Eastern USA and fly a constant 'due east' you do get to Europe eventually, via a Great Circle route. But this is a much longer route than the path usually taken which goes much closer to the pole. I suppose you could do that on a compass by changing the heading by N degrees every M minutes. A compass also doesn't take drift into account, so you could be dozens or hundreds of km off after your crossing.

We were crossing the seas centuries before GPS, INS or really any other form of modern technology.
All you need is a clock, a compass and a sextant. And some largely-forgotten skills, like how to do math without a smartphone.

Surely you can use a smartphone if you put it in flight mode.

Did the Vikings not have Calculator apps on their smartphones, or something? :p

We were crossing the seas centuries before clock (that would of use on a rolling ship) too—first chronometer sufficiently accurate to be of use for navigation was only created in 1761.

And I don't think Vikings already knew about compass either. Neither did Polynesians.

US Navy ships train on sextant navigation and practice it every day

In the days before GPS, we routinely crossed the oceans using inertial navigation systems.
The system I was familiar with used 3 separate inertial systems (Carousel was the brand name). You could choose to navigate by any single one, but the most common way of using them was to have the autopilot "average" the positions. You could also choose to exclude any given INS, in which case if you were averaging, you were averaging only two.
For the North Atlantic MNPS airspace system, You manually updated each INS passing over your last known ground position fix. When you passed over your first ground-based nav fix on the other side, you again manually updated the INSes with that information and then recorded in the maintenance log how far off left or right each INS was in the maintenance log. There were standards. Offhand I'm not sure I am remembering them correctly, but what I seem to recall was a max error of 2 nautical miles per hour flown without update. The MNPS had at the time a max error allowed without penalty of 10 nautical miles left or right of course. If that was exceeded, points were deducted from your company's score. Lose enough points and the company would not be allowed in fly in MNPS.
Off course errors of two to six nautical miles for a crossing were typical.
There is the story, true or not I do not know, of the captain who, when hand held GPSs first became available, used one to cross the North Atlantic, and had a near zero off course error. When ATC complimented him on that, he blurted out that he had used his hand-held. He was subsequently violated for using a non-approved navigational system. Whether the incident really happened, I don't know, but an airline's FAA approved op specs specifies not only which navigation methods are to be used but also which systems by brand and model name (at least back when I was flying).

At least until the early 2000s hand held GPS sold in the US would lock out at 99/199knots to prevent you using them in aircraft. The makers were scared they would be sued. To use them for an airborne science experiment we had to buy special FAA grade GPS

Most aircraft cross the atlantic by GPS, usually with INS as backup. INS as the primary form of navigation is still used as well.
Historically, a combination of dead reckoning and long range radio navigation systems were used on transatlantic routes. These include Decca, LORAN C and Omega.
Omega was shut down in 1997, Decca in 2000 and LORAN C ceased in 2010.

LORAN C/eLORAN is still in operation in some parts of the world...

They do use GPS, with backups, as the other answers describe.
If your question is inspired by MH370, remember that GPS tells you where you are: it doesn't tell anyone else where you are. GPS works by having a bunch of satellites sending out signals and, based on the signals you hear, you can calculate your own position. A GPS user doesn't transmit anything back to the satellites. What MH370 lacked was a system that was reporting its location back to base.

Thanks, I did know that about GPS, this wasn't inspired by MH370. I was just wondering how it would be done in aircraft without GPS ;)

Mode of air navigation I've witnessed:

Celestial - sextant and charts. Like, no kidding, right out of days of sailing ships.
Atmospheric pressure - driving along specific barometric pressure lines. By no means a primary form of navigation.
Omega - now obsolete. Triangulates on a small number of very powerful radio transmitters spread around the globe. At least good enough to hit the ADIZ w/in limits. I'm told when particularly close to a transmitter it can be as accurate as A Cat 2 ILS beam.
Inertial Nav -
GPS. what's that?

Omega were effectively high power NBDs. Pretty accurate if you knew how to use them properly. Of course pilots could also tune their NBDs to commercial stations with known locations (as the ill fated B-17 group did that flew into Hawaii on 7 December 1941) and get the same effect.

Are you referring to Non-Birectional Deacons?

Speaking of commercial stations... At about 100 miles east of Hawaii we could tune our NDB to KRLD, Dallas Texas. Why we could routinely pick up this particular station 3,600 miles away is a mystery to me. Maybe it was some dealership option package for these Texas Air National Guard airplanes.


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Which companies develop software for airplane systems?
I am wondering which companies develop software for systems on airplanes?
I am a software engineer major and I would love to work with planes in some way. I am not sure if that would be more of an electrical engineering position or not, any input would be greatly appreciated.

This entire branch is known as  avionics (aviation electronics). Limited work is generally done by the aircraft producers themselves, and the majority is subcontracted to specialist companies. A name which does come to mind is Thales group, who are behind much of the Airbus A380 avionics. Other ones are Rockwell Collins, Honeywell and Garmin. These are however though often at the top of an iceberg of various subsystems and controls.

A huge increase in this field (particularly in small aircraft but now also coming to larger ones) has been in tablet computers and the like in the past few years, and while I'm not a pilot I think it's hardly at the limit of what is possible. An iPad has more processing power than most if not virtually all aircraft flying today. Many customers today are disappointed if they don't get WiFi and inflight entertainment onboard.
With the increase in drones and unmanned aircraft, it's certainly not a shrinking field. A large area of this includes complex calculations and plenty of sensors. And more drones and unmanned aircraft require advanced communication and control systems. I've even heard about dynamic models of aircraft who adapt the plane's control to maintain control in the event of structural failure or serious damage. Only having scratched the field personally it's a very broad field with plenty.

Not to mention military applications (missile control, targeting software, etc.).  I'm fairly sure that the big airplane companies like Boeing and Airbus do a fair amount of their own programming as well even though they use a lot of prefabricated components.

An iPad has more processing power than most if not virtually all aircraft flying today.  I assume that you are talking only about GA?  Military and commercial craft have far more processing power, not to mention reliability and quality.

As Manfred mentioned, there are quite a number of companies that develop systems for aircraft, all with a software component to it. Whether it is something for you depends a lot on your expertise as a software engineer. Are you doing embedded programming then avionics might be a possibility for you. But you have to realize it is kind of a specialized field that is very strict in its procedures for safety reasons. If you enjoy rapid development processes and see quick improvements you are destined to become very frustrated in the avionics world. It is not a job I would recommend to everyone.
That being said, there are plenty of other software jobs related to aviation. Airports, Air Traffic Control, airlines, maintenance organizations all run dedicated software to support their processes. I did quite some programming in the past for Air Traffic Control related simulations. Nothing safety critical, the focus was on validating new ideas, which in my view was much more fun than working on operational (safety critical) systems.

I wouldn't recommend ATC software development over Avionics if you want to avoid strict procedures... but there are certainly some very interesting modelling and experimental/concept things going on around both avionics and ATC, if you don't want to create the actual "make the plane fly" avionics or "stop the planes crashin" ATC software

GE Aviation develops some avionics in addition to engines and other systems.

Are (were) you linked to that company? If so, please disclose it.

They had a location near where I used to live. I am not a shareholder and have never worked there.

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Would failure to put on an oxygen mask during loss of cabin pressure result in death?
I was trying to explain to someone why the cabin is pressurized (no one wants hypoxia) and that led to discussion about the emergency oxygen masks available on airliners.
If a person didn't put on their oxygen mask, would they be able to survive the lack of oxygen while making an emergency descent to a safe altitude? Would they sustain severe brain injury?

A very detailed discussion can be found in Linda D. Pendleton, When Humans Fly High: What Pilots Should Know About High-Altitude Physiology, Hypoxia, and Rapid Decompression (courtesy of xkcd).

I wonder if there's a risk of decompression sickness from losing cabin pressure.

@AdamDavis, the article linked to by Jan goes into that.

The most interesting point in that article is something that I always wondered: if I can hold my breath for 30sec, why do I have to put those masks in such a hurry? The answer: because you won't be able to hold you breath, the air pressure is so diff. that you can't not expel your air.

This SE answer is useful.

A young and healthy person? Almost certain to recover fully, given that altitude chamber training to 20-30k feet is routinely performed for a longer per-session time than the <4 minute rapid emergency descent. But there are always going to be a few people who are on the edge, one quick jolt away from death, who will croak. And it may not always be obvious who these are.

I did high altitude training about three months ago, up to 30,000 feet simulated altitude.  Here's the timeline:

Within 30 seconds (oximeter 100-95): noticed physical symptoms beginning.  I could tell that something was wrong, but felt functional.

Within 60 seconds (oximeter ~90): mild headache.  Still able to write my name.  Not feeling good, but acceptable.

Within 3 minutes (oximeter ~80):  Able to do simple tasks when specifically directed (thread a nut onto a bolt), but completely unable to multitask at even the simplest things (tried to put my pen down...didn't notice that I missed the desk - it landed on the floor.)

Within ?? minutes (oximeter ~70): I am no longer able to perceive the passage of time.  No longer able to take meaningful notes.  My signature is still legible - instinctive muscle memory apparently doesn't degrade nearly as fast.

Within 6 minutes (oximeter unknown): I have taken another pen from my pocket and am playing the knife game from "Alien" with it.  This is much more interesting than paying attention to the directions from the instructors.  I don't notice anything odd about my behavior.

Immediately after:  An instructor gives me a direct command to put my mask on.  I comply.

Total time in chamber: 7 minutes.  Time of useful consciousness in chamber: about 2 minutes

So, to answer your question: It depends.  I can safely say that seven minutes at 30,000 foot environment won't guarantee death (because I've survived it), and it won't guarantee severe brain injury (they let me keep flying) but on the other hand, I'm young and I exercise.  The best answer I can give is the same one that applies to scud running:
Just because the guy before you was able to do it, doesn't mean you'll be able to do it.

Very entertaining and educational (a bit heavy on bold text, though) :D  ... are there any advised breathing techniques that will prolong the process?

30,000 ft. isn't very high compared to typical airliner cruise altitude days.

Anecdotal, there are people who climb Mt. Everest without oxygen (29,0029ft or so), which would be somewhere into the hours of conciousness.  That being said, they usually talk about feeling high the whole time and, frankly, most mountaineers thinks those people are crazy, so...  Take it as you will.

@JayCarr they're also climbing Mt. Everest - we can assume (a) they're in superlative physical condition - though I'd agree with the other climbers about questionable mental status, and (b) they're taking quite a while to make the ascent, allowing their bodies to adjust to the pressure change. The relatively quick transitions in a high-altitude chamber (or the nearly instant transition in an explosive decompression) don't offer the same opportunity for your body to adjust.

@yankeekilo - I wouldn't have had to use so much bold if StackExchange hadn't disabled the <blink> tag.

@SteveV. that explanation makes me glad you were "forced" to use bold :)    I agree though - nice write-up!

@voretaq7 - Excellent points, both of them.  It would make sense that a rapid decompress would shock your body quite a bit more than gradually building to it.

BTW did you doodle your gravatar during the final phase of that test?

@yankeekilo - Don't be ridiculous. The story of how I doodled that gravatar starts out "There I was, inverted on the ILS, chief pilot in the jumpseat, doing formation flight with the space shuttle..."

When I did altitude chamber training, we simulated a rapid decompression by sitting in the vestibule, decompressing the main chamber, and popping the door to bring the vestibule down to what I think was a 25,000 foot cabin altitude. While there is some shock, it's not enough to incapacitate you, and it's certainly obvious what just happened - the whole area fogged rapidly. Quick-don masks make it pretty easy to get back on oxygen.

@JayCarr it's totally due to their intense acclimatisation program they are able to survive at altitude. I recommend reading Into Thin Air by Jon Krakauer, detailing more about climbing Mt Everest with everything screwing up in the end.

Very interesting. I love the term "Useful Consciousness"... I've been on the phone to some people today who would fail to qualify.

Short answer? It's entirely possible that not putting on a mask could result in death.
Long answer:
The classic example of hypoxia is the Payne Stewart Learjet crash that happened in 1999; the jet lost cabin pressure (and the crew lost consciousness) sometime in the 6 minutes between 23,000 feet and 36,500 feet. All 6 aboard perished in the crash.
From the NTSB report, which the Wikipedia article quotes:

Research has shown that a period of as little as 8 seconds without supplemental oxygen following rapid depressurization to about 30,000 feet (9,100 m) may cause a drop in oxygen saturation that can significantly impair cognitive functioning and increase the amount of time required to complete complex tasks.

There are tables available that show time of useful consciousness. Above FL300 (30,000 feet, or around 9,150m), a healthy human will have less than 3 minutes of useful consciousness. Prolonged hypoxia, at any altitude, can have serious repercussions. The National Institute of Health states that "[some] brain cells start dying less than 5 minutes after their oxygen supply disappears. As a result, brain hypoxia can rapidly cause severe brain damage or death" (source).

I'd vote for Helios 522 as 'the classic', with lots of supplemental oxygen, and a bus-load of people, yet they were all incapacitated and no one made it out alive. It happened a couple of years later though.

Pilots didn't know the pressure was too low and passed out on Helios 522. Although the hypoxia is not the cause of death, slamming into the side of a hill is. Hypoxia at that altitude would usually result in an irreversible coma.

@ptgflyer So if those people on Helios 522 were somehow magically rescued, would they be vegetables?

Sure, vegetables.

That would depend on at least the following:

how high the cabin got during the process
how long it stayed high
the physical condition of the passenger
perhaps to some degree how much oxygen was coming out of the masks of adjacent passengers

I went through NASA's altitude chamber program at the Johnson Spaceflight Center back in the early 80s. They wouldn't take the chamber higher than 25,000 for civilians. I was in very good shape back then (hard to believe now) and stayed functional the longest, but when they finally told me to put my mask back on, they told me I only got it half way to my face. An instructor had to come over and assist me.
Did I suffer brain damage? Some might contend I did.
Seriously, I Googled "survivability at high altitudes" and saw lots of info.

The other answers focus on the physiology of failing to put a mask on, but I am going to offer another take on this.
Whether you die from not putting on a mask depends on one thing: Did the pilots get their masks on before useful consciousness ran out?  If they did, you live.   If they didn't, you die.  It is as simple as that.  In the case the pilots get their masks on and no one else does, they will initiate an emergency descent.  This descent is typically initiated from memory items and not a checklist, so it can be initiated quickly.  The goal of the emergency descent is to be at 10,000 ft iASAP (for us the goal was under 4 minutes), and many jet aircraft can get there faster.  The only regulations I am aware of regarding the descent is that you must be below 25,000 ft in under 2 minutes (25.841; assuming complete loss of cabin).
If the emergency descent is initiated and in all likelyhood it won't matter if you put the mask on or not, you'll wake up during the descent and it'll only have been a few minutes.  Its always better to put the mask on, but it won't be the deciding factor, the pilots masks will be.
I'll also point out the O2 masks the pilots have are vastly different than those the passengers get.  Pax get chemical O2 generators that last about 15 minutes once activated (by pulling the tubing down) and attatch with a flimsy rubber band.  The pilots get quick-don masks fed by an O2 cylinder.  To don the masks you simply grab it, the O2 pressure inflates the webbing around the mask. Then you slip it on your head, let go of it and the mask compresses around your face.  Twist the mask regulator to Emergency and you have positive pressure forced flow O2 for the descent.

§25.841   Pressurized cabins.
  (a) Pressurized cabins and compartments to be occupied must be equipped to provide a cabin pressure altitude of not more than 8,000 feet at the maximum operating altitude of the airplane under normal operating conditions.
(2) The airplane must be designed so that occupants will not be exposed to a cabin pressure altitude that exceeds the following after decompression from any failure condition not shown to be extremely improbable:
(i) Twenty-five thousand (25,000) feet for more than 2 minutes; or
(ii) Forty thousand (40,000) feet for any duration.

What regulation requires you to be below 25,000 feet in two minutes?  I was going to write an answer similar to this, which is more the real answer to the question asked, but couldn't find the emergency descent rule. I thought that you had to reach 10,000 feet in four minutes or less, but apparently I was wrong....

@Lnafziger I added a reference for the 2 minutes to FL250.  I was also taught the 4 minute to 10k figure and this is what we used at my 121 carrier, but I cannot find a reference for it.  121.333 has a reference to 4 minutes but it deals with O2 requirements for flights at certain altitudes and the ability to descend in that timeframe.  Still looking!

@Lnafziger and I should add my interpretation of the 2 minute figure is a bit of a stretch, as complete rapid decomp is probably "extremely improbable" and the quoted reg excludes those cases.

@Lnafziger as best I can tell, the 4 minute rule may arise from avoiding the need to carry something more substantive than short-lived chemical O2 generators for the pax for high altitude flights.

I suppose FAR 135.89 mandating at least one pilot being on oxygen above FL120 doesn't apply to airliners? I find that super-surprising...

@JeffBridgman I dont have the reg handy, but we were only required to be on O2 if the other crewmember was not in the cockpit (two pilot ops).  Also, you'll find the regs pertaining to airliners in part 121.

One point here:  There are spots in the world where the 10k time limit can't be met.  Normal planes stay out of such places but some special flights go there--and have much beefier oxygen systems to compensate for the fact that descent in the event of depressurization isn't an option.

@LorenPechtel Sounds interesting. I assume mostly because of mountains. References? Maybe this is worthy of another question?

@bitchaser Some areas of the Himalayas--sometimes 10k is a long ways away.  If you want to do something like one of those sightseeing flights that goes around Everest you need the beefy oxygen systems.

@Loren Pechtel Just take a scheduled line to Leh. Not that small airport (several scheduled a day + military) and you are above 10k on the ground. No special planes., just several airlines. The flight will probably not kill you, but it may kill some sensitive people.

25000 feet: Most people will be gasping but probably conscious. Pulmonary oedema a risk.  10,000 feet - O2 is > 50% of sea level (50% is  ~= 14000 feet) -> Most people seated will be entirely happy. Some few may die :-(. I had a friend who got into trouble on Kilimanjaro around 10,000-12,000 feet - well below the 19,000 foot summit. He was medivacced and died next day in hospital :-(. He and we thought he was a fit and well 50 ish year old. Apparently not.

@RussellMcMahon altitude sickness is much slower than a few minutes. And a fit 20 year old is no less susceptible.

@KevinKostlan Yes. Steve V's answer gives a good guide to short terms . (Sample of 1).

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Is air in the toilet isolated, to prevent seeping into the cabin?
This made the news few days ago:

British Airways flight to Dubai forced to return to Heathrow due to 'smelly poo in toilet'

As can be seen at The Telegraph and The Independent.
Made me wonder: isn't it possible to recycle the air from the cabin and perhaps isolate the toilet? This could lead to a whole new series of chemical attacks on long flights.

Did you read this question? It shows that any airflow through the toilet just goes into the waste tank and then to the outside.

Yes, but I'm more interested in a quick change of all the available air inside the airplane, since it seems that the smeel was so bad... why wasn't that done, since a small part of the solution to the problem would be that.

Couldn't the pilot have deployed emergency oxygen masks...and continued with the journey...

@Firee - I do hope you're being sarcastic with that comment.

@Jamiec : No. The oxygen masks would have given the crew some more time to fix the situation. Spray some air freshner etc, or as a last resort, pilot could have dumped the poo mid-air over sea, like dumping fuel.

@Firee If im not mistaking: They only last for 15 minutes.

@AlexanderJohansen Yeah, and then if they actually did have a pressurization problem, it would be quite a problem indeed.

there is a latch only controllable on the outside to prevent pilots accidentally dumping poop. At those altitudes,  it will freeze mid air and become very dangerous to people and property below when it falls at high velocity

If someone can get chemicals on board a flight, they can also get a bomb on. Bombs are easier to make and more effective. Better air-conditioning won't help here, better security will.
It is possible to isolate the toilet... but the problem apparently wasn't just inside the toilet. The toilet isn't pressure sealed, so some smell will escape regardless. It's impossible to completely seal the toilet from the rest of the aircraft, and could be potentially dangerous if it was
The aircraft does introduce fresh air into the cabin, but the compressors to do so only have a fixed capacity. The capacity of these could be increased, but at the price of extra weight, fuel consumption and cost, it's not worthwhile for the 1 time in 100 million that a flight has to turn around for this reason. Even with higher capacities, it's not possible to just constantly flush the cabin air - and remember that all that air needs to be compressed (to maintain pressure) heated, and filtered. All of that costs more money, and adds more complexity, weight etc.


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What happens when a turbo-prop is over-torqued?
What does one need to do when a turboprop engine gets over-torqued?
I haven't over-torqued an engine before, but it seems it could happen inadvertently, say while doing a go-around.
My questions are:

Why is important not to over-torque an engine?
What happens if you do over-torque an engine?

This short answer is that you could break something if you over torque the engine.  And that's really about all that we can tell you in general terms.  The manufacturer or an engine repair shop could tell you what is most likely to fail for a particular model, but the failure modes won't be consistent from engine to engine.
As far as what to do if you were to over torque one, refer the the aircraft flight manual.  They will have a limitations section, and most airplanes will have "transient" limits in addition to the "normal" limits.  For instance, the limitation could be 100%, with a transient limit of 103% for 10 seconds and 105% for 5 seconds.  If the transient limits are exceeded, then you (or more likely a mechanic on your behalf) would need to refer to the maintenance manual for instructions.  Depending on the severity of the exceedance, it can be anything from simply logging it in the engine logbooks to a complete tear down and overhaul of the engine.
I'll also add that some pilots lean towards pretending that the exceedance never happened, and hope that nobody noticed.  This is not a good idea for several reason, the main one being that something could have been damaged that is not immediately obvious.  Even though things are running correctly now doesn't mean that all is well, and if an inspection is required, it's for a reason.  Another issue is that a lot of modern engines are computer controlled and monitored.  The next time that the computer information is downloaded, maintenance will see the exceedance anyway and if you have flown it since then you could be in even more trouble.
In short, follow the AFM procedures for your airplane.  They are there to help keep you safe!

You shouldn't over-torque an engine because you can stress parts more than they're intended to be and cause accelerated wear, or possibly damage or failure.  Modern turbines are designed well past their published limits though, so over-torquing does not necessarily mean anything was hurt, it depends on how far over it went, and how long it lasted.
If you do over torque an engine, the first step is to determine (if possible) how much the limit was exceeded.  What happens next is determined by how much the limit was exceeded.  Up to a point, nothing needs to be done.  After that, varying levels of inspection might be required.  Beyond a certain point, part replacement or rebuild/overhaul might be required.  What exactly happens is specific to each engine.

By exceeding the torque limits of the engine you rush shearing the driveshaft or damaging the propeller gearbox.  Not a good thing to have happen with the engine running at full power and rebuilds of these components are expensive.

If you were in trouble and pushed it to the firewall, A) be glad you are alive and B), you are looking at a tear down.  If not, your next flight might be your last.  Don't report it and someone else has a problem ..or loss...YOU may be looking at criminal charges,. particularly with today's computer recorded engine/system flight data.

Other than being in tension with the existing answers, this adds nothing but hyperbole to what's already been posted. DV on that basis.

Looks like Jeff and Joel need a lesson.  Not an issue.


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What happens when the logbook of an aircraft is lost?
If the logbook for an aircraft is lost, how does one replace it? Is the airplane still airworthy?

One thing I know for sure is that the resale value of that aircraft goes down pretty significantly.

you might want to start from here: http://www.coolinglaw.com/Content/UploadedFiles/Documents/Articles/Aircraft%20Logbooks%20.pdf

would photographs of each page of the logbook count? seems like it would be easy to just photograph every new page.

In order to state the plane is airworthy you must be able to show that all AD's have been complied with and that the aircraft is within annual (or 100 hour) inspection; these proofs are typically found in the logbook so no, without the logbook your aircraft is probably not airworthy. It may be possible to fly the plane legally in the US anyway if you receive authorization from your FSDO (which, I believe, would be a "ferry permit").
It's not legally required that your logbook be complete to the beginning of time, just that it shows the current requirements are met (along with the signatures/cert numbers of the AI's that are stating them to be met). However, an incomplete logbook is very important from a resale point of view. Not having complete logs will make a plane very difficult to sell and will certainly affect the price most purchasers would be willing to pay.

As mah pointed out, if you lose all your logbooks your aircraft/engine/propeller/avionics are no longer airworthy because they lack the documentation of required inspections, AD compliance, etc.
Everything is still "airworthy" in the sense that the aircraft doesn't know anything about paperwork and will happily fly, and getting a special flight ("ferry") permit from the FAA so you can take it to a mechanic to fix the paperwork will be pretty easy, but if you just go flying and something goes wrong the FAA and your insurance company will be most displeased about the lack of required paperwork.
In addition to the aircraft turning into a paperwork-pumpkin two things happen when you lose logbooks:

The value of the aircraft drops (I've seen aircraft selling for 30% less because of missing logs)
You have to "reconstruct" the aircraft's history and demonstrate compliance with all ADs and required inspections (an annual, an ELT check, a transponder check, a pitot/static check for IFR, etc...)

There's really not much you can do about #1 -- Logbooks are the history of the aircraft (and engine, propeller, avionics, etc.), and someone buying an aircraft is going to want to know that history.

How much a missing logbook matters is a matter of the buyer's personal opinion and what's missing. For example, I bought a plane missing Engine Log #1 (of 3). The engine has had two overhauls by well-known shops, one documented in Log #2 and one recently in Log #3, so my mechanic and I were not too concerned about the contents of Log #1.
  Had the first airframe log been missing (which documents the plane's life as a flight school trainer in Florida) there would have been a more substantial impact on the aircraft's value.

As far as #2 goes, "reconstructing" logs is usually pretty hard.
If you're the first owner, you've always used the same shop, and your mechanic keeps meticulous records they may be able to print you out a replacement log of everything that's ever been done to the aircraft and sign it off with no sweat.
If you're not the first owner but everyone who's owned the aircraft kept meticulous records (shop invoices, etc) you still have the history even if it's not in "logbook" format -- it won't satisfy the FAA, but it will make the process of inspecting the aircraft and determining its airworthiness a little easier for your mechanic.
If you're not in either of those situations your mechanic is going to have to give the aircraft a thorough going over (in addition to conducting an annual inspection they will need to verify that every AD has been complied with (or doesn't apply). That can be a very time-consuming (and expensive) process - particularly if there are many "inspection" ADs.
Other details about the aircraft's history can usually be reconstructed from your national aviation authority & accident investigators (in the USA you would do an N-number & Serial Number search in the NTSB aviation accidents database, and request the aircraft record from the FAA which will include things like FAA Form 337 for major repairs, alterations, and STCs.

Is '337 forms' a type of form, or a boatload of forms?

@cpast FAA Form 337 is the form used to report "major" repairs or alterations (such as rebuilding a wing after a ground handling incident).

It's important to know what an aircraft's logs are for - what they evidence, to understand why it's such a big deal when logbooks are lost.
To legally fly in the US (and UN/ICAO member territories), an aircraft must have a valid Type Certificate. This certificate signifies the aircraft's design meets legal requirements. Alterations, including significant repairs, require a Supplemental Type Certificate. STCs amend the original TC. STCs are filed with the aviation authority, and can be requested by anyone.
Modifications must be installed by a certificated A&P, aviation-speak for 'licensed' airframe and powerplant mechanic. Whenever a mechanic works on an airplane, they must make a logbook entry describing the work performed, the procedures followed, and the result (was the work accomplished successfully). The entry must include their certificate number.
The Type Certificate is valid only when accompanied by a logbook related to the airframe's serial number. So, every airplane must have an airframe logbook. If the airplane has engine(s), each engine must have its own logbook. If an engine has a propeller, the propeller gets its own logbook, too.
Each part installed in accordance with the STC installation document must be manufactured properly. This means it was made by an authorized manufacturer (PMA) and that manufacturer attests the part complies with the necessary specifications. Compliance is indicated by the 8130 form, commonly called a 'yellow tag'. They used to be born yellow, but given the age of most general aviation aircraft, most turn yellow in time.
Airplane designs are imperfect. These design flaws are usually found in mundane ways, but sometimes they make the news. When the flaw is moderate, the manufacturer issues a service bulletin, which is highly recommended, but not necessarily mandatory. If the imperfection is serious, the FAA issues an airworthiness directive, usually referring to the service bulletin. Airworthiness directives are mandatory, and must be addressed within a certain number of flight hours or some similar measure. These directives can require a one-time effort (e.g. replace a bolt with a differently spec'd bolt) or they can be recurring (inspect this part for cracks every 100 flight hours).
FAA regulations also require a thorough annual inspection of the aircraft. This must be performed by an extra-experienced A&P mechanic, one with 'inspection authorization'. The inspection must follow the aircraft's FAA approved maintenance manual. The results of the inspection are documented with entries in the various logbooks, including which revision of the manufacturer's inspection procedure was followed.
If the aircraft will be flying under instrument flight rules, the altimeter system must be tested every two years. This test must also be logged.
Although all of these logbooks are not required to be in the plane during flight, they must be made available for inspection if requested by an authorized person -- usually an FAA representative. Without these logbooks, the fed will issue a citation and possibly suspend the pilot's flying privileges.
It is interesting to note the pilot is ultimately responsible. The owner, as far as the FAA is concerned, has little responsibility. Although the owner may be sued in civil court, the pilot will receive the FAA's wrath.
So, if you lose your airplane logbooks, what do you do? You can request the type certificate and STCs. You must then attempt to reconstruct as many records as possible. You can review your emails and invoices. You can contact the places you purchased repair parts. However, if you cannot prove compliance with applicable airworthiness directives, you must re-perform the procedures required by the AD - like replacing the bolt, or inspecting the wing spar for cracks.
All of this will be costly, even by aviation standards. For old aircraft without historic value, it can be better to sell the plane for parts.


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How do I renew/revalidate my lapsed JAR PPL?
I obtained a JAR PPL in 2003 and flew regularly for a few years afterwards. My last flight as Pilot in Command was around 2006 and as I have not kept up the required number of hours per year since then I'm assuming my license will have lapsed.
What do I need to do to regain my PPL? Will I need to retake the exams, the radio telephony license, and the Skills Test?

I'll have a go at answering this.  It's confused by the UK's transition from the JAA to EASA licensing.
My JAR-PPL(A), issued in 2011, is valid for 5 years so yes, I assume yours will have expired.  My FRTOL is valid for 10 years so presumably yours will have expired too.
The requirements are hidden in CAP 804 ([Deep breath] Section 7, Part B (Schedule 7) Part C, Section 2, Paragraph 9-(1)(c)).  Renewing an expired licence (single-engined/single pilot aeroplane) seems to require meeting FCL.740.A of Part-FCL (type rating) and Appendix 9 to Part–FCL (skills test).
I believe this effectively means you'll have to undertake training to ensure you can pass the skills test, pass it and pay to have your licence reissued.  (Not forgetting the medical.)   You will end-up with a part-FCL PPL (which do not expire).
I'm not sure about having to retake the FRTOL tests, I think you may just have to re-sit the theory (PPL comms), fill out a form and pay but the answer is probably in CAP 804 somewhere!
The easiest/best thing to do would be to pop-in to your local friendly FTO and discuss with them...

Thank you, good answer and points to the resource I need to read.


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What is the reason aircraft are as long as they are wide?
I've noticed most aircraft are as long as they are wide from nose to tail and from wing tip to wingtip, particularly private jets despite recent swept wing technology. You can almost draw a perfect circle with a compass if you could find the centre.  Is it for aesthetic purposes, principles of flight aerodynamics or any other reason.  Please explain

Perhaps you are just looking at a too-limited set of aircraft?  E.g. sailplanes and cargo planes like the C-130  have a much longer wingspan than length; many jet fighters (the F-104 being the classic example) have wingspan shorter than length.

Swept wing technology is recent? Maybe in the late 1930s it was, being publicly unveiled at the 1935 Volta congress in Rome, but certainly not since maybe the last 60 years.

By curious coincidence it is simply what the optimal aspect ratio for speeds around 250–280 knots indicated results in. Aircraft designed for different cruise speeds have different ratios.
The wing span is governed by desired cruise speed. There are two main forms of drag—induced and parasite. Induced drag decreases with wing span and with speed, while parasite drag increases with them. So at lower speed, you need long wings to keep the induced drag at bay, while parasite drag is low simply because of the low speed. And at higher speed, you need shorter wings to avoid too much parasite drag.
Jet aircraft are most efficient at transsonic speeds (Mach number 0.75–0.85) and altitudes around 10-12 km (33,000–40,000 ft) and it so happens that the wing span and cabin length to contain corresponding payload are similar. Turboprop aircraft are most efficient at somewhat lower speeds and altitudes and consequently their wings are a bit longer. And yet slower piston-powered aircraft have even longer wings relatively to fuselage.
(update, as suggested in comments): The extremes are on one side gliders that achieve low drag by having very long slender wings and flying slow and on the other side supersonic aircraft that have short wings with long chord to keep the frontal cross-section low, the very extreme being the very fastest aircraft like X-15 or SR-71.

You could add a glider and the F-104 as examples for the extremes. Airliners are in between.

@PeterKämpf, it's strange why F-104 in particular has such short wings when it's not all that fast, just ~M2.0. Other M2 jets have still quite a bit bigger wings.

@JanHudec The F-104 was, for a time, the fastest plane in the world, so part of the explanation may be "first attempt to build something that fast." Even today, the F-15 is the only USAF plane that's faster (in terms of air speed, rather than mach number). Also, as an interceptor, its primary mission was presumably to fly at maximum speed, whereas the F-15 is also required to do other things.

@qqjkztd: Hey, the fuselage alone is 3.05 m long. And then the winglets reach a little further back. See here for proof.

Propellor cargo planes are another exception to the 1:1 length/wingspan ratio: e.g. the "Spruce Goose" at  218' 8" (66.65 m) long by 320' 11" (97.54 m) wingspan, C-130 at 98' long, 132' wingspan, Martin Mars at 118' long by 200' wingspan.

@jamesqf, that's definitely not another exception. They are simply propeller-driven planes.

@Jan Hudec: How are those not exceptions to the 1:1 length/wingspan "rule"?  My arithmetic says they are, and if you think about it, you might guess that the reason is that they're designed to produce a lot of lift at relatively low speed.

@jamesqf, they are exceptions. They are not another exceptions, because they are already mentioned in the answer.


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Can a mid wing airplane have no wing spar running through the fuselage?
Can a mid wing be attached to a fuselage such that no features of the wing run through the fuselage? (so that the pilot can seat comfortably and close to the center of gravity) Airplanes such as the mini max has its wings bolted to the sides. Does that mean there is no main spar running through the fuselage and connecting both wings?
If it is possible, can it be done on the cri cri by Michael Colomban? And what would be the necessary adjustments to the fuselage?

Possible duplicate of How is a wing joined to the fuselage?

Yes it can, albeit at the cost of some added weight.
By using reinforced bulkheads, the bending loads can be transferred into the bulkheads which leaves the center section free of structure. That is how large engines and their intake ducts can be placed where normally the spar would go. A classical example is the Lockheed F-104 Starfighter.

Lockheed F-104 Starfighter cut-away drawing (picture source).
Using bracing like on the Mini-MAX reduces stresses in the carry-through, but does not remove the need for something to keep the wings apart. In other words, the compression member of the wing spar is still required to transverse the fuselage where the wings are attached. Also, at high angle of attack the wing produces substantial nose thrust which could fold the wings forward were it not for a second compression strut at the wing nose.

Mini-MAX 1100 (picture source)
In case of the Cri-Cri, which is a low wing design, the pilot sits on top of the spar. Moving the wing up to a mid position would create a much heavier aircraft and would require a wider fuselage, too.

 Colomban Cri-Cri (picture source)

Wow! That explains it. I was wondering how a bulkhead not joined at the top would resist all that bending forces. Thanks a lot  peter kämpf.


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What is the moderate dihedral angle for a low wing airplane?
An increase in dihedral results in a decrease of the total lift produced by the wings. I would like to know the moderate dihedral angle (in degrees) for a low wing airplane, especially the amature built kind( for instance the rv-3).
Also, is there a recommended angle of attack for such category of airplanes.

By "moderate", do you mean "average" or something like that? "Moderate" just means "not unusually big or small" so there is no single "moderate angle", just as there is no single height of tall people.

To the angle-of-attack question:
It appears you are thinking of airplane design recommendations. In that case, I wonder if you are thinking of wing incidence angle or decalage angle, which are design choices, while angle-of-attack varies as the plane flies.
Wing incidence is the built-in angle between the wing chord and the airplane center line (which in many cases is parallel to the propeller's thrust line). The wing incidence angle, relative to the thrust line, influences what happens when you add or reduce engine power. You normally want a slight positive trim change (nose pitches upwards) when adding power, but not too much.
Decalage is the difference in incidence between the wing and horizontal stabilizer (the wing should always have a larger incidence angle than the stabilizer). A large decalage angle generally makes the airplane more self-stabilizing in pitch, but it also causes larger trim changes when airspeed is increased or reduced.
Angle-of-attack is the angle between the wing chord and the "relative wind" the airplane flies in. It is not set, but varies from slightly negative up to the stall angle of attack, depending on the airplane's airspeed, wing loading, and the lift coefficient of the wing's airfoil. High speed and low wing loading results in a near zero angle-of-attack, even negative for a high-lift type of airfoil, while low speed and high wing loading results in a large angle-of-attack.
The designer normally sets the wing incidence angle so that during normal cruise conditions, which typically imply a wing angle-of-attack of 0-2 degrees, the fuselage sits approximately horizontally, i.e. neither tail low or tail high. In this way the air resistance of the fuselage is minimized during cruise.
Aerobatic airplanes and other agile airplanes typically have a zero-zero setup (both incidence and decalage angles close to zero). This gives high maneouverability and small trim changes as the airspeed changes. The downside is that the stability is low. "The aircraft goes where you point it" and has little inbuilt stability, so it has to be actively flown all the time.
If this sounds complex, it is. Some more on the subject is found at: https://www.av8n.com/how/htm/aoastab.html

Please do not worry about the loss in lift. It is real, but so small that it can be neglected. A poor flap or aileron seal will cost you more in L/D than the dihedral ever will.
The loss is proportional to the difference of the cosine of the dihedral angle to unity. With 5° (which is on the upper end of typical values for low wing aircraft) this is just 0.38%.
The exact amount of dihedral depends a lot on details of the configuration:

Aspect ratio of the wing
Fuselage size relative to wing root chord
Wing sweep
Directional stability

In general, you need a good balance between $c_{l\beta}$ (dihedral effect) and $c_{n\beta}$ (weathervane effect).


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How does engine noise change during descent / approach?
When on the ground beneath a STAR transition I hear commercial jets making a dramatic change in sound. I assumed it was the sound of high-bypass engines being pulled back at stepdown fixes, but when a friend recently asked me what the sound was, I wanted to make sure I was providing the correct answer. I am familiar with the sound made by the Fuel Over Pressure Protector (FOPP) cavity on A380s but this is a different, much lower pitched and shorter duration sound. Any help?

very good question!  I will be very interested in the answers we get...

They just let off the clutch too quickly ;)

Not sure this "duplicate" is helpful, I don't understand what is the correct answer (Doppler, sound absorption, sound speed vs altitude, flaps extension). I believe anybody is able to identify the Doppler shift without knowing the name, the two answers of the duplicate don't bring much other information in detail (and none has actually been selected). Maybe it's time to build a good focused answer.

Can you post a recording of the sound you're hearing?

Would this answer your question?

@SMSvonderTann OP stated that he was already familiar with the sound made by the FOPP, which is what that question deals with.

Is the sound specific to that location, or is it similar to another place under an aircraft route?

Could you make a video of the sound? That may help us.

It is important to notion that an aircraft does not provide a uniform sound but features several sources of noise. The noise generated by the individual sources has separate characteristics and is transmitted into different directions.
For example, the sound of the engine front fan is sent into the direction of flight, creating a cone. The sound of exhaust jet and low-pressure turbine is transmitted backwards. Passive sound sources sent according to their positioning on the aircraft. Underside structures transmit downwards.
When you experience an aircraft transition overhead, the sound created by the aircraft may be steady but you experience the sound of changing sources.

I think you will often hear the engines spooling up and down on final because they are adjusting altitude, and they might be coming in too low or high so they have to adjust accordingly.
Also flaps and gear are extended in the final because the glidepath is quite shallow which cause more drag, so to keep the airspeed where it should be and not higher (for safety) the engines need to put out more thrust, thereby causing the extra noise heard on final. In the initial descent, you probably are gliding with the engines at idle causing more drag than thrust. It is the most efficient way to descend in a jet.


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Should the pitching moment be up or down?
I had a question regarding the direction of the pitching moment.
To make sure we are on the same page, here is what I know so far (please correct me if I am wrong).

Lift acts through center of pressure
Normally moment is taken around Aerodynamic Center because then the moment does not vary with angle of attack.
In a cambered airfoil, the aerodynamic center and center of pressure are not at the same place, so the lift created also generates a moment at the aerodynamic center.
In a symmetric airfoil, the aerodynamic center and the center of pressure are at the same place, so you do not have a pitching moment.
Location of Aerodynamic Center is fixed for an airfoil, it does not change with speed.

I am trying to understand the concept of longitudinal static stability and in all the diagrams, the pitching moment is shown to be nose up.

But I would imagine that the center of pressure is further downstream on a airfoil than the aerodynamic center, so shouldn't the pitching moment be nose down? As shown in this picture

Thanks for your help,

you can have a moment computed around any arbitrary point. There is a  center of gravity, a center of pressure and aerodynamic center. 3 different things, but really, the rotation of an object depends on the moment computed around whatever is the hinge (in this case center of gravity)

@Radu094, you are right except that there is no 'hinge' on a flying aircraft. For our mathematical convenience, we may consider all motion as rotations around CG plus whatever translation there is, but if you try to isolate pure rotation, its centre could be anywhere. A delta wing airplane can have centre of controlled pitch rotation outside in front of the craft (which may confuse pilots), due to strong force from elevons. An isolated normal wing, with its initial lift (CP) at ¼chord and CG at ½, will start pitching up about a point midway between the two.

The diagram above is for an aircraft with the Center of Pressure (CP) IN FRONT of the center of Gravity (CG).  in this case the pitching moment is indeed Nose up. But this makes the aircraft statically unstable. Only one aircraft (AFAIK) is like this, (the F-16) and it is only like this when subsonic.  It can deal with the instability because it is "fly by wire" - the computer constantly generates stabilator inputs to compensate.   Most all other aircraft have the CP behind the CG and then the pitching moment is indeed nose down.

All points you mention are correct (for the nitpickers: Point 5 is only true below transsonic speeds). That the pitching moment of the wing is drawn nose-up is probably because it is positive this way - nothing more. The sketch you posted in your question is rather poor, with the center of gravity located behind mid-chord when it should be closer to the aerodynamic center.
Indeed, if you have positive camber, the center of pressure of the wing is behind the aerodynamic center, so the wing's pitching moment around the aerodynamic center should be nose-down. However, if you assume the center of gravity of the isolated wing to be at mid-chord, the center of pressure is normally between the quarter chord and mid points, so the wing all by itself will pitch up because it pitches around the center of gravity. The moment depends on the reference point.
Did you look at this answer for an explanation of static stability yet? Let me know if something is left unclear.

Thanks, for the reply, indeed if you want longitudinal stability, the change in lift at  the rear has to be more than at the front!

@T-REX: Yup. Simple, isn't it?

@PeterKämpf "the aerodynamic center is normally between the quarter chord and mid points, so the wing all by itself will pitch up because it pitches are" Did you mean center of pressure here? Or perhaps meant to say something else? Because a pure moment imparts the same direction of rotation no matter where it is relative to the COG. Direction of rotation changes though if it is a translating force being applied at different locations around the COG (ie. not a pure moment).

Or maybe you are referring to the aerodynamic force acting at the aerodynamic center? But then you would need to qualify that the lever arm between the COG and aerodynamic center is enough for the force to overcome direction of the pitching moment at the aerodynamic center.

@DKNguyen OMG, you're right. Stupid mistake, thank you for pointing this out!

@DKNguyen makes a great point along with Peter Kampf's great knowledge of the subject.  An applied force will move an object if applied at the CG, or rotate it if it is off-center.  No doubt there.  But once it moves, the center of pressure comes into play, again at the CG.  Both diagrams are poor.  Generally, the torque force of the wing lift pitches the nose down, requiring opposite torque from the tail for level flight.  Doesn't the addition of the tail and fuselage move the Aerodynamic Center of the entire aircraft rearwards anyways?

@RobertDiGiovanni Is aerodynamic center even defined for an overall aircraft? I'm not sure that it can be from my understanding of the definition. I think it's highly probably it can only be defined or a single airfoil.

One of the joys of scratch building is to take a brand new wing by itself and let it tumble through the air.  Adjusting weight helps, but adding a tail makes it much more stable.  We all have our definitions.  I would not disagree that AC pertains to a single airfoil.

For the pitching moment, two distinct cases need to be considered, the airfoil and the whole aircraft, both over a range of Angle of Attack (AoA). The questions centre around the main wing only, the picture in OP is of an entire aeroplane, creating some confusion.

Airfoil. A positively cambered airfoil indeed contributes a nose-down pitching moment, as mentioned by @quietflyer. The magnitude of the pitching moment varies with AoA, as depicted in the graph below.

Note that the graph plots $C_m$ as function of $\alpha$ (AoA), and moment M = $C_M \cdot \alpha$.
A constant $C_M$ means that the pitching moment varies linearly with AoA.
For this wing and for many others, $C_M$ is constant when the moment axis point is chosen in the Mean Aerodynamic Chord of the wing. The sign of $C_M$ is negative: nose down. The moment axis point can be chosen anywhere on the wing, but the point where $C_M$ is constant proves to be a very convenient definition point and is called the Aerodynamic Centre.

The whole aircraft. The aircraft must be longitudinally stable, meaning that the aeroplane returns to a trim position after it encounters an aerodynamic disturbance. The moment equilibrium of the whole aeroplane is considered around the Centre of Gravity (CoG), because this is where the response movement hinges around. There are many more parts of aircraft contributing to the pitching moment equilibrium, as the picture below from this answer illustrates - for clarity reasons, the X-axis origin point is chosen in front of the aeroplane.

The M.A.C. is depicted away from the CoG. The M.A.C. is also the imaginary centre point for the wing lift force $N_W$, which increases with AoA. For the total aeroplane, that equates to a nose up pitching moment contribution of the main wing in flight, where $N_W$ is not zero.
The horizontal tail contributes to the pitching moment with force $N_H$. In the picture this force points up, contributing a nose down pitching moment. This answer states the situation where a horizontal tail upforce results in a longitudinally stable aeroplane.
For the aeroplane in trimmed position, the total pitching moment is zero. If it encounters an aerodynamic disturbance its AoA changes, and return to the trimmed position means that $C_M$ as function of AoA must be negative.
Longitudinal stability must be considered in the complete range of AoA and sideslip, including stall. In and around the stall the moments and forces cannot be considered linear. It is vital that should the horizontal tail partially stall, for instance in a tight sideslip, the nose pitches down - so at low speed, the aeroplane is trimmed around the CoG such that the tailplane delivers a downward force.

But I would imagine that the center of pressure is further downstream on a airfoil than the aerodynamic center...

Introducing centre of pressure confuses the whole picture, since it changes with AoA and we cannot construct a pitching moment situation that is valid for a wide range of AoA. Best forget use the Aerodynamic Centre instead in generalised considerations of stability and control.

the pitching moment is shown to be nose up

Peter alluded to it in his answer, but let's explicate it:
In the cases I have encountered, the clockwise (nose-up) circular arrow drawn just indicates the direction of a positive $M$.
However, the actual moment is negative in typical flight regimes, so, as you say, nose-down.
Just like the tail lift $L_t$ is drawn with an arrow pointing up, indicating that positive $L_t$ corresponds to upward tail lift, even though for many aircraft the tail lift in typical flight regimes is downward, ie negative.


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Why are commercial flights not (publicly) trackable in some locations?
Flying BA15 from London to Sydney, I noticed that the flight is not tracked over Turkmenistan and Afghanistan, except for a short ping.
Is this for security reasons? Do planes disable their ADS-B, or is the data somehow restricted? Since position tracking is a safety feature, is this regulated or an airline decision?

Related (not a duplicate): Do flight tracking websites also track non-commercial and defense aircraft?

The reason is that there is no member of the general public in those areas with an ADS-B receiver sharing live data with the public tracking sites.
Websites like Flight Radar 24 rely largely on volunteers installing ADS-B receivers and sharing their received data. They have a good coverage, but some areas are still not covered.

In other words, those websites rely on people who have nothing more important to do, are interested in aviation and/or radio, have reliable Internet access, and are rich enough to be able to afford said Internet access plus an ADS-B receiver. It should not come as a surprise that the population density of such persons is higher in Western Europe than in Afghanistan, for example.

There are also many countries where even receiving radio transmissions is illegal if you're not the intended recipient.

Some of these sites actually provide the equipment for free if you commit to setting it up and operating it in an area where they need more coverage (for example https://www.flightradar24.com/apply-for-receiver). The legality is probably the bigger issue with those empty spots on the map.

@StephenS ADS-B is a public broadcast, though. It's intended for everyone to be able to receive it. Such a law would not apply to it.

@MichaelHampton Law might apply to private, unauthorized ownership of ADS-B receiving equipment, though. I wouldn't want to have a strange looking antenna in Iran right now, especially if the explanation is "it keeps track of airplanes". As a similar example: https://blog.telestial.com/2017/11/countries-where-satellite-phones-banned-or-restricted/

Flightradar24 actually has instructions for a Pi-based DIY receiver. The receiver dongle costs about 30 USD and supposedly covers 200-400 miles. So the whole thing runs at less than 100 USD. Not a major investment. https://www.flightradar24.com/build-your-own

@Someone, not a major investment for a first-world country, which is why there's great coverage even in the vast empty reaches of the United States, but $100 for the receiver plus the cost of an always-on internet connection is quite a bit in a place like Afghanistan.

@MichaelHampton The U.K.'s OFCOM apparently does not share that view. ATC transmissions are similarly broadcasted in the clear, but OFCOM's official position is that people other than ATC, pilots, and such are not "intended recipients" and are not allowed to listen to those transmissions, record them, or share them with anyone else. This is why liveatc doesn't operate in the UK.

@reirab I suppose I should not be surprised that Ofcom has such a view. They are, after all, effectively the UK's censorship agency. At least I learned something new today.

@MichaelHampton Yeah, personally I find OFCOM's position to be totally insane, but it's their position nonetheless. If someone wants a transmission to be 'private' in 2020, they're not going to use in-the-clear narrow-band AM... For that matter, if someone wanted a communication to be private in 1950, they would not have used in-the-clear narrowband AM.

@reirab The same applies in Germany: listening to ATC is not allowed to the public. But possible...

@reirab I mean it's not really Ofcom's view that matters here; it's the law. The law says you're not allowed to receive radio signals for which you're not the intended recipient. This law dates back to when encryption was impractical for most users, but it hasn't been changed.

@Muzer It's up to OFCOM to interpret and enforce it, though, no? If one wanted to be that literal about the meaning of "intended recipient," the other aircraft on frequency are also breaking the law when they listen to ATC's instructions for another aircraft. That being said, I've read official statements from OFCOM saying that they support the absurdly outdated law in its current form and its continued enforcement. That's more the part that I consider insane.

@reirab fair enough then! Ultimately enforcement for personal use is likely to be nonexistent (especially since there isn't really any technical way of detecting it).

@Someone: In 2015, the threshold for "extreme poverty" was defined as "income of less than 1.90$ per day" by the World Bank. About 734 million people (or about 10% of the population) fell below this line. And note that while someone who earns 2$/d does not fall under this definition of extreme poverty, they are still pretty effing poor by most people's standards. So, for a significant portion of the world's population, 100$ is a pretty major investment, indeed. It is the difference between their whole family having food for weeks or even months or all of them starving to death.

@PerlDuck But doesn't a cleartext broadcast signal literally match the description of publicly accessible information of Art. 5 GG?

@reirab Obvious workaround: get your pilot's license so that you can run your ADS-B station. Alternately, get a patch of grass in a field and call it a "private helipad". ;)

@Muzer the data appearing on a tracking website would be PROOF that SOMEONE is receiving and processing it illicitly. Openly colluding with such an operator could have severe consequences for the website operator, depending on where they are running that website from.... especially since it could be argued that they are undermining aviation safety!

@nick012000 how would that authorize you to share that data with the general public?

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is it OK to move a light aircraft by pushing or pulling the propeller?
It's very common to see pilots moving a light aircraft by pushing or pulling on the prop, either because there's no tow bar available or simply out of preference or convenience. Is this a reasonable thing to do or can it damage the prop or engine in some way?

does someone want to do the math on how much force needs to be applied to move, say, a 3368 pound airplane (my MTOW) forwards or backwards?

My first suggestion would be to read your POH to see what it says!  The answer may vary by aircraft model as well (especially geared -vs- non-geared engines).

A couple of my CFIs have asked me to help them park the airplane (in absence of a tow bar) when I was pushing the airplane by putting one hand on the hub and the other on the propeller near the hub, and them (the CFIs) pushing the tail down and nose wheel elevated. But according to AOPA, it is not a good thing:

... never push or pull on the prop blades. Forget what anyone has told
you about pulling near the hub or the strength of the propeller.
Aluminum blades can bend, and it doesn’t take much to put the blades
out of track with one another.

This PDF says the same thing:

Avoid pulling the airplane around by the prop. Yes, this seems the
perfect solution to a vexing problem of how to change the airplane’s
position without having to walk around and get the tow bar, but it’s
worthwhile to make the extra effort. Neither the engine nor the prop
particularly benefit from the loads imposed by horsing the whole
airplane around.

The FAA says in AC 20-37E

Do not push or pull on propeller blades when moving the aircraft by hand. Tow bars are specifically designed for this operation.

At my old flight school (Hillsboro Aviation) they also taught me this.  However, at Riddle the ramp is large enough that all airplanes can taxi without being towed at all.  This is probably to minimize any potential problems towing - such as what you mentioned.

Isn't "horsing the whole airplane around" what the propeller does during powered taxiing? The blades may not like asymmetric loads from handling, but transferring the force from pulling on the axle is exactly what the engine and bearings are made to do, isn't it?

@HenningMakholm They are made to pull the plane straight forward, but not to push it backward or to one side or the other.

Are the days of moving a prop and having the engine kick over loooong gone?

@HenningMakholm during powered movement it's the air pushing on the propeller blades, there's a maximum force that can exert, and it's fairly even on the whole propeller. I'll bet that pushing on a blade (especially on a tip) is more than the air could do.

Classic example of one corner case leading to a blanket belief.
Grabbing a propeller by the tip, especially a wooden prop, can cause damage. In use, the tips generate most of the thrust but are also held straight by the rotational forces.
Pulling on a prop right beside the hub will cause no harm - that's where the propellor thrust goes anyway. If you grab the prop on both sides the airframe won't know that the engine isn't running.
So, here's a Rule of Thumb: if you cannot touch the prop hub with your thumb while pulling on the prop, you are holding it too far out.

A literal rule of thumb.

I would add that I usually only do this when I'm moving the plane straight forward or back. If I have to turn it, I get out the tow bar (although I admit to kicking the tire left or right to make small adjustments).

Well, grabbing the propeller at the blade root and pulling from there cannot hurt it. Why? Because the thrust imparted by the propeller to the aircraft is applied at exactly the same place. In other words, the propeller pulls the airplane through the air at the hub. You are so close to the hub that you're not going to create a significant bending moment along the blade.
On the other hand grabbing the propeller at the tips would be questionable at best, and ill-advised!

I asked around at my gliding club about this, the consensus seems to be that it won't harm the plane as long as I didn't use excessive force.
The reason for doing it is to not have to walk from wing to wing to move the plane.  The main counterpoint is that you shouldn't move a plane by yourself unless you're very sure you won't hit anything (another plane, the hangar walls, etc).

The main counterpoint for most propeller-driven singles I'm familiar with is "There's a towbar, it's designed to move the airplane, and you should use it!" :-)

That's true, but at my club all the planes are either taildraggers or private planes with wooden props.
Personally, I always get another person (or two) and push/pull by the wing struts.

Yeah, taildraggers are a slightly different beast, and I imagine wooden props are less prone to being pulled out of track than metal ones (?). They do make taildragger tow rigs, they look like a lot more effort but I'd try to use one in preference to manhandling the prop :)

I can't help but see irony in asking a gliding club about this.

We have our own hangar that's big enough for the tow planes, the club-owned fiberglass ships, and some members' private airplanes.

As always with these questions it seems to be a religious thing. If you ask 2 people you will have at least 3 different answers and most of them will sound somewhat reasonable.
I had the situation that my FIs always taught and asked me to move the planes (taildraggers) with me pulling the plane on the prop and them steering using the rudder. A few days ago another guy walked up to me when I moved the plane shouting at me "NEVER do this, you'll destroy the prop"
So I called the technical support of the specific airplane (Diamond Aircraft) and asked them.
TL;DR: Manufacturer says that's exactly the way they move the planes in production when they don't have the tow bar around.
For reference: The plane has an electric constant speed prop so I guess about the most fragile you can find in terms of prop.
Of course you should always grab as close to the spinner as possible
One can verify plane specifically this from POH or AMM, for example Diamond DA 62 AMM states:

I know this thread is 4 years old but I could not find the questions answered anywhere else and the question comes up on a regular basis esp. in clubs where "knowledge" is passed on from member to member.

Thank you for the reference. I also looked it up in the DA20 manual and it even states you should rotate the plane towing on the prop: "If no  tow-bar is  used, during forward traversing the nose-wheel will  follow the  movement of the airplane. Change in  direction is achieved by  pulling on the propeller hub" (http://support.diamond-air.at/fileadmin/uploads/files/after_sales_support/DV20_Katana/Airplane_Flight_Manual/Basic_Manual/40102-r3-DV20-AFM.pdf, Section 8.4.1)

How do you taxi your plane? I use my engine to spin my propeller, which pulls on the hub and pulls my plane hard enough to make it roll on the ground. On takeoff, I do this so hard that the 2000+ lb plane rolls 60 knots or so before it leaves the ground.
Now, with that in mind, do you think pulling on the prop, close to the hub, enough to move the plane 10 feet is doing any damage?

By deviating from the standard procedure (using the tow bar) you incur into the following risks:

Mechanical damage: you risk damaging propeller itself if you don't pull from as close as possible to the hub. Furthermore, being more complex, variable pitch blades obviously imply more risk.
Arguably, the forces in play during taxiing are similar to those exerted manually through pulling. Also, in my flight school, during pre-flight inspection we actually perform some push/pulls to assess that the propeller, hub, and drive are ok -- suggesting that there is no mechanical stress derived from doing so.
Safety risks: although arguably rare, you may accidentally start the engine through hand-swinging. I was instructed in my flight school to shut down the engine through the mixture control mainly to prevent this from happening during the pre-flight inspection previously described. This is also why we perform magneto ground checks during shutdown.

Maybe on an 80HP J-3, but you ain't hand propping my 270 HP high-compression TIO-540cu engine

Regarding "it must be ok to pull the plane by the prop because the prop pulls the plane through the air"...
Yes....through the air. The air is much less sticky than the ground.
Also, the propeller doesn't pull the plane through the air, it pushes air behind the plane creating a lower pressure area in front of the plane and a high pressure area behind it. This "pulls" the plane into the low pressure area.

"Yes....through the air. The air is much less sticky than the ground." It also pulls the plane while moving on the ground (ie. taxiing). Also, the depiction of the pulling force as a result of a pressure difference is not very accurate.

The cause of the pulling force is not significant - the fact is there is a pulling force applied to the blades which is then transferred to the hub and crankshaft, which is transferred to the engine mounts, then the airframe, etc. What is different is the lack of rigidity in the blades when they're not rotating at high RPM. That lack of rigidity means you could bend them (or their attach points) much more easily by pushing on them. Which is why it's important to apply any force as close to the hub as possible - but not on the spinner itself!


text:
When did inflight smoking become (widely) prohibited?
Currently in my mid-'30s, I can still clearly remember the time when half of the plane's passengers were smoking throughout a long-haul flight. I know commercial flights became non-smoking sometime in the late '90s but I can't remember the exact timeline and the Wikipedia article is remarkably lean in details.
When did the major airlines start forbidding inflight smoking? How long did it take for the new policy to spread across most of the airlines? Can we expect this length of transition period to apply to other significant policy changes (e.g. the use of small electronic devices being allowed during take-off and landing by some airlines, provided they are in flight-safe mode)?

end 90's begin 00's IIRC

See also: Is it legal to smoke in your own plane?

There is an interesting timeline here which includes other transportation service as well.
According to this New York Times article, the FAA banned smoking on all flights under 2 hours beginning April 23, 1988. According to the timeline, Northwest and British Airways make all domestic service smoke free shortly after.
On February 25th, 1990, the rule is expanded to all domestic flights under 6 hours, which includes all but 28 of 16,000 flights.
In 1992, ICAO urges its members to go smoke free by July 1, 1996. Delta went smoke free on all flights starting in 1995. TWA, United, and American follow suit in 1997. In 1998 even more airlines go smoke free.
This federal rule bans smoking on all flights to and from the US and is effective June 4, 2000. It mentions that all domestic and 98% of international flights were already in compliance.
td;dr The FAA banned smoking on all flights under 2 hours in 1988, and it escalated from there. Within 10 years, almost all airlines were smoke free.
I think that smoking had the advantage of being a health issue, whereas electronic devices are more just convenience and comfort. Barring any emergent safety issues, it seems easier to allow people to do something new (use electronic devices) than stop them from doing something (smoking). Considering the proliferation and advancement of inflight entertainment systems, I would expect airlines to be fairly quick about allowing the use of devices, especially since some already do (I know American and United do).

hmm, as one reason for airlines to disallow electronic entertainment devices is to protect their income from renting out access to the in flight entertainment systems (many airlines still demand payment for getting rental headphones for their custom sockets, and some have pay per view movies and games among other things), I'd see the bans on electronics increase rather than decrease as more airliners have built in personal systems that can be charged for.

@jwenting- The ban on electronics isn't per airline though, it's per the FAA.  And once it's completely lifted (which it mostly has been at this point) good luck to any airline that wants to ban electronics.  People like their personal devices, and given a choice between an airline that let's them use their own iPad v. one that doesn't...I think they'd choose the one that lets them use their own device.  The free market would take it from there.

Some airlines also let you use your own device to connect to their entertainment system where you can pay for TV, movies, or Internet.


text:
What is the weight budget of a fully loaded A380?
Wikipedia provides some numbers (typical empty weight, MTOW, max fuel capacity, etc.), but I can't seem to find more detailed figures. For a purpose of this question, let's assume a fully loaded A380 in typical 3-class configuration (~530 passengers) and fuel for a long haul flight (>10h).
So, what is the typical weight of the passengers + luggages? Is any additional cargo typically carried? If so how much? What about the weight of crew and catering? And fuel weight? (Fuel weight will depend on actual flight duration, so the answer should mention the corresponding flight duration.)

These weights are all based on the maximum an aircraft will ever see. The maximum allowed weight of passengers (+luggage) and cargo (called payload weight) is the difference between the Operational empty weight (about 270,000 kg) and the Zero fuel weight (361,000 kg). This means the payload weight is about 91,000 kg. The passenger and crew weight can be estimated by the following numbers:

175 lbs per pax + 30 lbs of baggage for short medium range distance (or 40 lbs for long range)
175 lbs per crew member + 30 lbs of baggage$^1$

So let's say that (for easier calculations) the average passenger + luggage weight is 100 kg.
When we assume 530 passengers and 25 crew, then the weight would be $555\times100=55,000kg$. That leaves 36,000 kg for cargo.
All the weights listed are, of course, maximum weights. That means that an aircraft in general does not meet these values.
The maximum fuel weight is the difference between maximum ramp weight and zero fuel weight (which is $562,000-361,000=201,000kg$). About 2,000 kg is taken for the time the engines are running while the aircraft did not yet take of (for taxiing etc). This is the difference between maximum ramp weight and MTOW.
The amount of fuel varies so much per flight that I really can't say anything about it. It depends on the air pressure in the flight path (aircraft choose their routes depending on that, for a faster flight), weather along the route, and much more. For quite a good overview I suggest for you to read this Wikipedia page.
I hope I answered your question sufficiently.
$^1$ Source: Jan Roskam, Airplane design, Part I: Preliminary Sizing of Airplanes (1985)

Maximum fuel capacity of A380 is listed as 323,546 l, which amounts to 262,072 kg of Jet-A1. Like in most aircraft, full tanks + maximum structural payload is over MTOW. In case of A380 way over MTOW. It means that the aircraft has longer range with less payload.


text:
Can I save money on becoming a helicopter pilot in the US if I do flight hours in Mexico?
Flight hours costs approximately $285 per hour. Below is a screenshot from a local (Newport Beach, CA) school regarding what it takes to become a private pilot.

So I was hoping that maybe there might be a school in a local country like Mexico where I could do that for less money. If so, are there any things that I need to take into consideration. Or how do I make sure that those hours will be applicable to my license to be able to fly in the US?

The US is one of the cheapest places in the world to learn to fly. Regulatory hurdles aside, Mexico is almost certainly more expensive. There are probably other US locations marginally cheaper than San Diego, but helicopter training is pricey anywhere.

As far as I can tell from the FARs as long as your training is performed by an FAA-certificated flight instructor and complies with the appropriate requirements of part 61 of the FARs you could theoretically do parts of your (primary/private) training anywhere you want, get all your endorsements, then come back to the USA to take your checkride and get a regular US (FAA) pilot's license for the appropriate category/class of aircraft.
From a practical standpoint I think this may be more work than the money you save.
If you do your pre-solo training in Mexico any instructor you come to in the US is going to want to fly with you a bit before they endorse you to solo.
If you try to do the whole thing in Mexico you would have to comply with Mexico's flight training requirements (Medical, student pilot certification, solo endorsements, etc. - about which I know basically nothing) as well the US FAA's requirements (like holding a US student pilot certificate with appropriate endorsements prior to taking your checkride).

Note that the procedure is a little different if you want to get a Mexican pilot's certificate and then convert it to a US/FAA certificate (that's all detailed in FAR 61.75 if you're interested. It doesn't sound like that's what you want to do, but at least as far as the regulations go that seems to be a more well-traveled path and something your local FSDO could probably advise you on - at the very least it would involve paperwork, possibly also a checkride).

I'd like to say a couple of words on Primacy since we're talking about training: Where you learn and the procedures you learn first will form the foundation of your aviation knowledge.
What that ultimately means for you depends on how different the regulations are where you do your training versus where you will do most of your flying. The FAA has been moving to standardize our procedures to be more in line with ICAO standards for a number of years now, but there are still differences and you may have to re-learn some of the regulatory bits of aviation if you did the bulk of your training elsewhere.
It makes sense to me to learn to fly where you intend to fly -- ideally in the same region (a sleepy corner of the midwest versus lower New York's airspace can be a culture shock!) but if cost is a factor find the best bang for your training buck in the airspace system you'll be spending most of your time in.


text:
What is needed to operate a LSA aircraft at night?
As a PPL holder in the USA, what do I need to have on the aircraft (or otherwise?) in order to be able to legally fly at night?  LSAs are much cheaper to operate, so it looks very tempting in order to be able to fly more hours, I'm just concerned about getting stuck out at dusk, especially in winter.

When I started flying the C-162 at night, the first thing I found was weird is the lack of a white tail-light.  Tail lights are required on "regular"/non-LSA planes, but somehow not required on LSAs.   I don't get why an LSA is allowed to be less visible than bigger planes. :)

Since you have your private, the LSA just has to be approved.
According to the FAA Order 8130.2G CHG 1 which covers LSA certification:

(5) This aircraft is to be operated under VFR, day only, unless
  appropriately equipped for night and/or instrument flight in
  accordance with 14 CFR § 91.205, and when allowed by the
  manufacturer’s operating instructions.

So it must be properly equipped (see below) AND allowed by the manufacturer’s operating instructions.   You will need to check this with each manufacturer to see if they certified it for night flight.
91.205 says day VFR instruments (paragraph b) plus:

(c) Visual flight rules (night). For VFR flight at night, the
  following instruments and equipment are required:
(1) Instruments and equipment specified in paragraph (b) of this
  section.
(2) Approved position lights.
(3) An approved aviation red or aviation white anticollision light
  system on all U.S.-registered civil aircraft. Anticollision light
  systems initially installed after August 11, 1971, on aircraft for
  which a type certificate was issued or applied for before August 11,
  1971, must at least meet the anticollision light standards of part 23,
  25, 27, or 29 of this chapter, as applicable, that were in effect on
  August 10, 1971, except that the color may be either aviation red or
  aviation white. In the event of failure of any light of the
  anticollision light system, operations with the aircraft may be
  continued to a stop where repairs or replacement can be made.
(4) If the aircraft is operated for hire, one electric landing light.
(5) An adequate source of electrical energy for all installed
  electrical and radio equipment.
(6) One spare set of fuses, or three spare fuses of each kind
  required, that are accessible to the pilot in flight.

Is there a line about using circuit breakers instead of fuses?

That is the reg verbatim, but the key is "of each kind required".  If none are required (because you use circuit breakers instead), them you don't need any fuses.


text:
What is the pressure distribution around a supersonic wing?
In subsonic flight the lift manifests itself at 25% of chord, but shifts to 50% of chord when the airplane goes supersonic.
Wondering about that made me think that the reason might be that there is high-pressure in front of the wing´s top-point like there is at the bottom in front of the low-point, and low pressure behind the low-point of the wing like there is behind the top-point.
Assuming a symmetrical biconvex wing profile, that would put the centre of lift the 50% of chord.
A symmetrical biconvex wing going straight forward would produce no lift, so it has to be put at an angle to compensate for the weight of the airplane and the Mach-tuck, but still the lift would manifest itself at 50% of chord "seen my way" - and that gets more and more the faster the plane goes as the AoA gets closer to 0.
A couple of extra questions: at what AoA is a fighter (F-16/18/22/35/Rafaele/Typhoon/Gripen) flying with in low (M 1.3) and high (M 1.8) supersonic flight?
Do fighters have symmetrical biconvex wings or do their wings have a camber?

I am confused about your question. Is it: What is the pressure distribution around a supersonic wing? or is it Do fighters have symmetrical biconvex wings or do their wings have a camber?

Sorry for not coming back until now, have been busy....
DeltaLima, it is both, but I guess it has been answered, and probably ought to have been asked separately....

Normally, supersonic fighter wings for which airfoil information is published use a very thin NACA 6-digit section with very little camber, such as
Aircraft                root airfoil      tip airfoil
McDonnell Douglas F-15  NACA 64A006.6     NACA 64A203
General Dynamics F-16   NACA 64A204       NACA 64A204
Lockheed-Martin F-22    NACA 64A?05.92    NACA 64A?04.29

This information is from The Incomplete Guide to Airfoil Usage by Dave Lednicer. As you can see, the F-16 uses camber throughout, indicated by the 0.2 design lift coefficient of the airfoil, while the F-15 uses an uncambered root airfoil.
Those airfoils are chosen because flow around them at supersonic flight speed is still heavily influenced by subsonic flow characteristics as long as wing sweep allows for a subsonic leading edge. This produces nose suction, and flow around the wingtips disturbes the pure supersonic flow characteristics even when the leading edge is supersonic.
How the idealised flow around a supersonic airfoil looks is explained in this answer.
The angle of attack in supersonic flight depends on air density and load factor, but generally is only a few degrees because drag increases with the square of angle of attack. In other words, if the plane flies at high angle of attack, it decelerates to subsonic speed quickly.
The angle of attack in straight flight depends on altitude, wing loading and aspect ratio and grows with decreasing air density. Normally, at low level the maximum dynamic pressure limit and engine thrust will only allow very low supersonic speeds around Mach 1.1 to 1.3. Only above 20.000 ft will the envelope expend enough to make flight at Mach 1.8 possible.
For a typical wing loading of $\frac{m}{S}$ = 300 kg/m² and Mach 1.3 at 10.000 ft (air density $\rho$ = 0.9 kg/m³, speed of sound $a$ = 330 m/s) the angle of attack is $$\alpha = \frac{2\cdot m\cdot g}{\rho\cdot (Mach\cdot a)^2\cdot S\cdot c_{L\alpha}} \approx 0.5°$$ with a typical lift curve slope of a supersonic wing of $c_{L\alpha}$ = 4.

Thanks, and the "angle of attack in supersonic flight" part of the question were with flying in a straight line in mind, how much AoA does an loaded fighter (F-16/18/22/35/Rafaele/Typhoon/Gripen or the like) have at M 1.3 and 1.8 going straight forward....?
It of course depends on what "Loaded" is, so lets say armed with what an F-22 can carry internally (8 A2A missiles) and 3/4 tank full of gas, it has spend some getting to altitude....;- )

A question about the wingloading you mention m*g/S, but then the units are N/m2, right? Usually it's expresed in kg/m2, I believe.

@ROIMaison Of course you are correct. Thank you for spotting this!

In general, the combat aircraft do have cambered wings. Most of the combat aircraft use NACA 6-series was designed for low-drag at transonic speeds, as this is where they spend most of their flight.
Take the wing of the F-15 Eagle for example. The wing root is symmetrical, while it becomes cambered going outwards. According to the report on CAP-TSD Analysis of the F-15 Aircraft:

The wing root is a 6 percent thick symmetric airfoil. The wing decreases
  in thickness towards the tip, which is a 3 percent highly cambered airfoil. The F-15 wing has conical camber outboard of he 20 percent semi-span location.

F-15 wing airfoil shape; image from CAP-TSD Analysis of the F-15 Aircraft
There are a number of reasons for using camber- most of their flight is in subsonic speeds anyway and having a cambered airfoil helps keep the aircraft more or less level, as the angle of attack is only a few degrees anyway; any further increase will incur a drag penalty due to the speeds involved.